std::shared_ptr::owner_before – cppreference.com

std::shared_ptr::owner_before

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<tbody> </tbody>
template< class T > bool owner_before( const shared_ptr<T>& other) const;
template< class T > bool owner_before( const std::weak_ptr<T>& other) const;
Prüft, ob diese shared_ptr other vorangeht Umsetzung Inhaber-basiert (zur wertorientierten Gegensatz) definierten Reihenfolge. Die Reihenfolge ist, so dass zwei Smartpointer gleichwertig nur wenn beide leer ist oder wenn sie beide eigene dasselbe Objekt sind vergleichen, auch wenn sich die Werte der Zeiger durch get () erhaltenen unterschiedlichen (zB sind, weil sie auf verschiedenen Unterobjekte innerhalb derselben hinweisen Objekt)
Original:
Checks whether this shared_ptr precedes other in implementation defined owner-based (as opposed to value-based) order. The order is such that two smart pointers compare equivalent only if they are both empty or if they both own the same object, even if the values of the pointers obtained by get() are different (e.g. because they point at different subobjects within the same object)
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Diese Reihenfolge wird verwendet, um gemeinsam und schwache Hinweise einsetzbar als Schlüssel in assoziative Container, typischerweise durch std::owner_less .
Original:
This ordering is used to make shared and weak pointers usable as keys in associative containers, typically through std::owner_less.
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Parameter

other -
die std::shared_ptr oder std::weak_ptr verglichen werden
Original:
the std::shared_ptr or std::weak_ptr to be compared
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Rückgabewert

true wenn *this vorangeht other, false anders. Gemeinsame Implementierungen vergleichen die Adressen der Steuerblöcke .
Original:
true if *this precedes other, false otherwise. Common implementations compare the addresses of the control blocks.
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Beispiel

#include <iostream>
#include <memory>
 
struct Foo {
    int n1;
    int n2; 
    Foo(int a, int b) : n1(a), n2(b) {}
};
int main()
{   
    auto p1 = std::make_shared<Foo>(1, 2);
    std::shared_ptr<int> p2(p1, &p1->n1);
    std::shared_ptr<int> p3(p1, &p1->n2);

    std::cout << std::boolalpha
              << "p2 < p3 " << (p2 < p3) << '\n'
              << "p3 < p2 " << (p3 < p2) << '\n'
              << "p2.owner_before(p3) " << p2.owner_before(p3) << '\n'
              << "p3.owner_before(p2) " << p3.owner_before(p2) << '\n';

    std::weak_ptr<int> w2(p2);
    std::weak_ptr<int> w3(p3);
    std::cout 
//              << "w2 < w3 " << (w2 < w3) << '\n'  // won't compile 
//              << "w3 < w2 " << (w3 < w2) << '\n'  // won't compile
              << "w2.owner_before(w3) " << w2.owner_before(w3) << '\n'
              << "w3.owner_before(w2) " << w3.owner_before(w2) << '\n';

}

Output: 

p2 < p3 true
p3 < p2 false
p2.owner_before(p3) false
p3.owner_before(p2) false
w2.owner_before(w3) false
w3.owner_before(w2) false

Siehe auch